Lecture Outline - Chapter 11

11.1 Skeletal Muscles (p. 222, Figs. 11.2, 11.3)
	1.	Skeletal muscles are covered by fascia that extends beyond their ends as tendons. The origin of a muscle is the end attaching to the immovable bone; the insertion of a muscle is the end attaching to the movable bone. Muscles are frequently grouped as synergists and antagonists. The muscle that works hardest is the prime mover. 
	2.	Functions of Muscles (p. 223)
		a.	Skeletal muscles maintain posture, cause movement, and produce heat.
		b.	Cardiac and smooth muscle are two other types of muscle. 
	3.	Skeletal Muscles of the Body (p. 224, Fig. 11.4, Tables 11.1, 11.2)
		a.	Skeletal muscles are named according to their size, shape, location, direction of fibers, number of attachments, or action.
		b.	Names and functions of the major muscles of the body are listed in Tables 11.1 and 11.2 on page 225 of the text.
11.2 Mechanism of Muscle Fiber Contraction (p. 227)
	1.	Overview of Muscular Contraction (p. 227, Fig. 11.5, Table 11.3)
		a.	The plasma membrane of a muscle fiber is its sarcolemma. Its endoplasmic reticulum is called the sarcoplasmic reticulum, which stores calcium. The sarcolemma invaginates into T tubules that contact the sarcophasmic reticulum. 
		b.	Myofibrils and Sarcomeres (p. 227, Fig. 11.6)
			i.	Myofibrils are cylindrical structures within muscle fibers. Myofilaments that make up myofibrils are arranged such that they exhibit striations.
			ii.	Striations are grouped into sarcomeres. Within sarcomeres, thick filaments are made up of myosin, and thin filaments are made up of actin.
		c.	Sliding Filaments (p. 227)
			i.	When a nervous impulse reaches a muscle fiber, the sarcoplasmic reticulum releases its stored calcium, and the fiber contracts. The myosin filaments have cross-bridges that pull on the actin myofilaments, causing them to slide past each other. 
			ii.	The sliding filament theory states that the filaments do not change in length as the sarcomere shortens.
	2.	At the Neuromuscular Junction (p. 228, Fig. 11.7)
		a.	A motor nerve fiber expands into a synaptic end bulb as it approaches a muscle fiber. When a nerve impulse travels down the neuron, synaptic vesicles storing a neurotransmitter move to the end of the bulb, releasing the neurotransmitter.
		b.	The muscle fiber receives the neurotransmitter at receptor sites. The sarcolemma generates impulses that travel over the sarcolemma to the T tubules and sarcoplasmic reticulum. Stored calcium is released to the cell, triggering contraction.
	3.	As Contraction Occurs (p. 229, Fig. 11.8)
		a.	Two proteins, troponin and tropomyosin, occur in conjunction with the actin filaments. Calcium binds with the troponin, exposing a myosin-binding site. 
		b.	Myosin cross-bridges bind to the revealed site on the actin filaments. ATP supplies energy to the cross-bridges.
11.3 Observations of Whole Muscle Contraction (p. 230)
	1.	Basic Laboratory Observations (p. 230, Fig. 11.9)
		a.	A myogram is the visual pattern generated from the recorded contraction of a muscle.
		b.	Muscle Twitch (p. 230)
			A single contraction is termed a muscle twitch. It is divided into a latent period, a period of contraction, and a relaxation period.
		c.	Summation and Tetanus (p. 230)
			When a muscle receives a rapid series of stimuli, it cannot relax between contractions. It contracts (summates) until it reaches a sustained contraction, called tetanus.
	2.	Muscle Tone in the Body (p. 230, Fig. 11.10)
		a.	Muscle tone results when portions of muscles are contracting while other portions relax.
		b.	Maintenance of muscle tone requires receptors called muscle spindles.
	3.	Recruitment and the Strength of Contraction (p. 231)
		When a nervous impulse is received, all muscle fibers within the motor neuron contract together in a motor unit. When more impulses are received, more motor units contract (recruitment).
	4.	Isotonic Versus Isometric Contraction (p. 231) 
		Isotonic contractions occur when a muscle tenses and shortens. Isometric contractions involve tensing, but not shortening, of a muscle.
11.4 Energy for Muscle Contraction (p. 232, Fig. 11.11)
	1.	ATP can be supplied to muscle in three different ways.
		a.	Aerobic cellular respiration can supply muscles with energy.
		b.	One anaerobic pathway uses creatine phosphate to regenerate ATP.
		c.	A second anaerobic pathway, fermentation, provides energy without using oxygen. Fermentation ends with lactic acid, which changes muscle pH, leading to fatigue.
		d.	If an activity is not too strenuous, the three pathways work together to supply energy.
		e.	In people that train, the number of mitochondria per muscle cell increases.
	2.	Oxygen Debt (p. 232)
		Oxygen debt occurs when cells have used up available supplies of oxygen. Repaying oxygen debt means replenishing creatine phosphate and converting lactic acid back to pyruvate.
		HEALTH FOCUS: Exercise, Exercise, Exercise (p. 234)
		i.	Exercise improves muscle strength, endurance, and flexibility, along with cardiovascular endurance.
		ii.	Exercise has been shown to prevent certain kinds of cancer as well as to increase bone mass.
		iii.	Guidelines for staying fit are given in Table 11A on text page 234.
11.5 Exercise and Muscle Contraction (p. 235)
	1.	Exercise and Size of Muscles (p. 235)
		a.	Atrophy occurs when muscles are unused.
		b.	Forceful exercise (weight lifting) increases the number of myofibrils in a muscle, leading to hypertrophy.
	2.	Slow-twitch and Fast-twitch Muscle Fibers (p. 235, Fig. 11.12)
		a.	Slow-twitch Fibers (p. 235)
			Slow-twitch fibers have more endurance and supply their energy aerobically. 
		b.	Fast-twitch Fibers (p. 235)
			Fast-twitch fibers are anaerobic and designed for strength but not endurance. They can develop maximum tension rapidly but fatigue quickly.
11.6 Working Together (p. 235)
	The Working Together box (p. 236) illustrates how the muscular system works with other body systems to maintain homeostasis.